The Structure of Dinichthys 



197 



gsS'S 



Text-figure 85. 

 Fragments of the fin rays of Dinichthys. 

 (Buffalo Museum specimen No. 15611/E2806). 



(1889). Newberry's specimen shows 7^8 "rays" in the natural position lying close tO' 

 ■gether. In the previously mentioned specimen described by Dean, the rest of the fin struc' 

 ture also is well preserved. A small specimen of Dinichthys curtus in the American Mu- 

 seum also has some rays in situ. In Text-figure 85 are pictured some fragments of rays from 

 the Buffalo Museum of Sciences (No. 15611/E2806). They enable one to see clearly the 

 structure of the single bones. As New- 

 berry has already mentioned, the rays 

 are only calcified on the surface. Their 

 inner parts were probably tilled with car- 

 tilage. Therefore they are always more 

 or less strongly flattened and crushed. 

 They are thicker and rounder at both ends 

 and narrower in the middle part. They 

 were joined together by the thicker parts. 

 The longer and more even spines described 

 by Newberry may have belonged to the 

 dorsal fins; the smaller, shorter, from 

 Buffalo, to the paired fins. 



The presence of a dorsal fin is dis- 

 tinctly indicated on Dean's specimen. It is in nearly the same place as in Coccosteus. 

 Also, fragments of the pelvic fins and pelvic girdle '-' of the same specimen make it evident 

 that Dinichthys, like Coccosteus, had these fins. Apparently the previously described 

 rays from Buffalo descend from these fins. 



It is much more difficult to decide whether Dinichthys, or rather all Arthrodira, had . 

 pectoral fins. As we know, on this point the opinion of scientists is sharply divided. 

 The older investigators, such as Miller, von Koenen, Trautschold and Newberry sup- 

 posed that the Arthrodira had pectoral fins just like other fishes. But the majority of 

 later scientists have come to the conclusion that the Arthrodira had the pectoral fins 

 either very strongly reduced, or not developed at all (Traquair, Woodward, Dean and 

 others). This opinion is, however, based exclusively on a negative character. In not a 

 single one of the thousands of specimens of Coccosteus or other Arthrodira hitherto known, 

 have there ever been found marks which could be explained as traces of pectoral fins. 

 Even specimens with well preserved spinal columns and pelvic girdles carry no fragments 

 of the pectoral fins. 



Jaekel, contrary to all the other investigators, in all his papers on the Arthrodira 

 since 1902 has advocated the opinion that the Arthrodira had pectoral fins. He had no 

 actual facts to confirm this theory, but only judged that the strongly developed pelvic 

 girdle made it very improbable that the pectoral fins were reduced. (Analogous cases in 



'• A short description of a new find in the Bull. Cleveland Mus. Nat. Hist. no. 33, 1926, confirms the presence of a back-bone in 

 Dimchthys. 



